Method and apparatus for scheduling a downlink packet in a wireless communication system

ABSTRACT

The present invention relates to a method and apparatus for scheduling a downlink packet in a wireless communication system, which preferentially appoints a combination of a traffic flow and a physical resource block (PRB) having a low per-bit transmission power requirement during real-time traffic scheduling, and allocates the remaining PRBs to non-real-time traffic using spare transmission power. For this purpose, the downlink packet scheduling method of the present invention comprises: an operation of performing real-time traffic scheduling, which involves carrying out the process of preferentially appointing a combination of traffic flow and a PRB having the lowest per-bit transmission power requirement; a step of performing non-real-time traffic scheduling, which involves allocating remaining PRBs, which remain after the allocation to the real-time traffic, to non-real-time traffic using spare transmission power.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a National Stage of International ApplicationNo. PCT/KR2011/004611, filed on Jun. 24, 2011, which claims priorityfrom Korean Patent Application No. 10-2010-0082474, filed on Aug. 25,2010, the contents of all of which are incorporated herein by referencein their entirety.

BACKGROUND

1. Field

Methods and apparatuses consistent with exemplary embodiments relate toa method and apparatus for scheduling a downlink packet in a wirelesscommunication system, and more particularly, to a method and apparatusfor scheduling a downlink packet, wherein a wireless communication basestation which has to send a plurality of pieces of user traffic to eachuser receiver (user equipment) through shared radio resources selects auser traffic flow to be transmitted in a downlink for each point oftime.

In other words, exemplary embodiments relate to a method and apparatusfor scheduling a downlink packet, wherein a wireless communication basestation which has to send a plurality of pieces of user real-timetraffic and non-real-time traffic in a downlink by using a limitednumber of physical resource blocks (PRBs), selects a user traffic flowthat will use PRBs in the downlink for each point of time of scheduling.

2. Description of the Related Art

In general, a downlink scheduler (i.e., a packet scheduler) plays a veryimportant role in determining system performance in a recent wirelesscommunication system using a packet switching method, such as 3^(rd)generation partnership project (3GPP) long-term evolution (LTE).

This is because the amount of downlink transmission resources islimited, whereas if a proper scheduling method is not used, there is adanger of deteriorated quality of service (QoS) for correspondingtraffic because downlink traffic experiences packet delay and a bufferoverflow due to its burst characteristic.

FIG. 1 shows a construction according to an embodiment for the downlinkof a wireless communication system in which exemplary embodiments areapplied.

In general, an element that plays an important role in order to provideQoS for user traffic, is the downlink scheduler (i.e., the packetscheduler) 13 of a wireless base station. User traffic flows (downlinktraffic) that have to be transmitted by the wireless base station in adownlink, as shown in FIG. 1, is stored in buffer memory 12 in whicheach traffic flow is designated by a traffic classifier 11. The downlinkscheduler (i.e., the packet scheduler) 13 determines which packets oftraffic flow, from among all the traffic flows, will be transmitted touser equipment 14 through wireless channels for every transmit timeinterval (TTI).

For reference, N_(PRB) PRBs are present within one transmit timeinterval (TTI).

Meanwhile, since the total data throughput of a system and QoS for eachtraffic flow are determined depending on what criteria are applied tothe process of selecting a traffic flow, there is a need for ascheduling method capable of evenly satisfying a QoS level requested byeach user traffic flow and also maximizing the total data throughput ofa system.

Representative scheduling methods, from among a variety of schedulingmethods proposed so far in order to satisfy the requirements, include around-robin method, a maximum through (MT) method, and a proportionalfair (PF) method.

Each of the scheduling methods is described in more detail below.

First, the round-robin method is a method of selecting a traffic flow tobe transmitted through each PRB according to specific sequence (e.g., insequence of increasing traffic flow index) if N traffic flows arepresent. In this round-robin method, radio resources can be fairlydistributed into all traffic flows because a transmission opportunitycorresponding to the share of each traffic flow is assigned to each ofall the traffic flows, but the total data throughput of a system is notoptimized because the capacity of a radio link that is different foreach user is not taken into consideration.

Next, the MT method is a method of selecting a combination of a PRB anda traffic flow through which the greatest amount of data can betransmitted because the traffic flow, from among traffic flows includingpackets to be transmitted in a buffer, has the best instantaneouschannel capacity of a corresponding wireless channel and assigning anopportunity capable of sending the packets through the PRB to thetraffic flow, as in [Equation 1] below.

$\begin{matrix}{\left( {\hat{s},\hat{n}} \right) = {\arg\mspace{11mu}{\max\limits_{s,n}D_{s,n}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, D_(S,n) is the number of bits that is assumed in a system and thatcan be transmitted by a traffic flows through a PRB n and is determinedbased on a channel state information (CSI) value of the correspondingPRB.

This MT method is advantageous in that it can maximize the total datathroughput of a system because a combination of a PRB and a traffic flowthrough which the greatest amount of data can be transmitted, but thereis a limitation in which the QoS or fairness of traffic flows is nottaken into consideration.

Next, the PF method is a method of calculating a ratio of the number ofbits D_(S,n) that can be transmitted through a corresponding PRB foreach traffic flow and the total data throughput R_(S) of a traffic flowthat has been transmitted according to results allocated right before aPRB as a priority function and selecting a traffic flow having thegreatest priority function, from among the calculated priorityfunctions, so that the traffic flow is transmitted through thecorresponding PRB, as in [Equation 2] in assigning a PRB.

$\begin{matrix}{\left( {\hat{s},\hat{n}} \right) = {\arg\mspace{11mu}{\max\limits_{s,n}\frac{D_{s,n}}{R_{s}}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

This PF method can be considered as a method of slightly compromisingthe total data throughput and improving fairness as compared with the MTmethod.

The limitation of the PF method, however, is that it is difficult toprovide QoS for a delay-sensitive traffic flow because packet delay isnot taken into consideration like in the round-robin method.

SUMMARY

Accordingly, the conventional techniques have problems, such as thosedescribed above, and thus there is still a need for a “scheduling methodcapable of evenly satisfying a QoS level requested by each user trafficflow and also maximizing the total data throughput of a system”. Anobject of the exemplary embodiments is to solve the problems and meetthe demand. The exemplary embodiments may solve some of the problems ofthe conventional techniques, or may not address any problems of theconventional techniques.

Accordingly, an aspect of an exemplary embodiment is to provide a methodand apparatus for scheduling a downlink packet, which are capable ofimproving the total data throughput and fairness of a system by using alimited number of PRBs and limited transmission power in the downlink ofa wireless communication system using an adaptive modulation and coding(AMC) scheme.

That is, an aspect of an exemplary embodiment is to provide a method andapparatus for scheduling a downlink packet, wherein a combination of aPRB, having the smallest transmission power required per bit whenscheduling for real-time traffic is performed, and a traffic flow ispreferentially selected and PRBs remaining after PRBs are allocated toreal-time traffic are allocated to non-real-time traffic by using excesstransmission power, unlike in the existing methods of determiningscheduling based on an MCS level (i.e., the transmission capacity of aPRB) determined based on CSI.

Aspects of the exemplary embodiments are not limited to the above, andother aspects and advantages of the exemplary embodiments that have notbeen described will be understood from the following description.Furthermore, it may be easily understood that the aspects and advantagesof the exemplary embodiments can be realized by means written in theclaims and a combination thereof.

In an exemplary embodiment, method includes, in a method of scheduling adownlink packet, the method comprising, a real-time traffic schedulingoperation of performing a process of selecting a combination of aphysical resource block (PRB) and a traffic flow, on all pieces ofreal-time traffic; and a non-real-time traffic scheduling operation ofallocating PRBs remaining after allocation to the real-time traffic inthe real-time traffic scheduling operation, to non-real-time traffic byusing excess transmission power.

Meanwhile, an apparatus of an exemplary embodiment includes, in anapparatus for scheduling a downlink packet, real-time traffic schedulerconfigured to perform a process of selecting a combination of a physicalresource block (PRB) and a traffic flow, on all pieces of real-timetraffic; and non-real-time traffic scheduler configured to allocatePRBs, remaining after allocation by the real-time traffic scheduler ofthe real-time traffic, to non-real-time traffic by using excesstransmission power.

The real-time traffic scheduling operation may comprise: a metriccalculation operation of calculating a scheduling metric forcombinations of the real-time traffic flows and available PRBs;selecting a combination of a real-time traffic flow and a PRB having amaximum calculated scheduling metric; and repeatedly performing all theprocesses on all the real-time traffic flows starting from thescheduling metric calculation operation.

The metric calculation operation may comprise calculating the schedulingmetric by using a ratio of an excess channel gain and reception powerrequired per bit.

The scheduling metric calculation operation may comprise calculating ascheduling metric M(s,n) for a combination of a real-time traffic flow sand a PRB n according to the following equation,

$\begin{matrix}{{{M\left( {s,n} \right)} = \frac{\Delta_{s,n}}{{f\left( b_{s,n} \right)}/b_{s,n}}},} & \lbrack{Equation}\rbrack\end{matrix}$

where Δ_(s,n) is the excess channel gain and f(b_(s,n))/b_(s,n)indicates the reception power required per bit.

The scheduling metric calculation operation may comprise calculating thescheduling metric according to the following equation,

$\begin{matrix}{{{M\left( {s,n} \right)} = \frac{g_{s,n} - {g_{\min}\left( b_{s,n} \right)}}{\sigma_{s,n}^{2}{w\left( b_{s,n} \right)}}},} & \lbrack{Equation}\rbrack\end{matrix}$

where g_(s,n) indicates a channel gain for the PRB n of downlinkcorresponding to the traffic flow s, g_(min)(b_(s,n)) indicates aminimum channel gain necessary to successfully send b_(s,n) bits,σ_(s,n) ² indicates a noise variance of subcarriers of the PRB n of userequipment corresponding to the traffic flow s, and

${w\left( b_{s,n} \right)} = {{\frac{1}{3b_{s,n}}\left\lbrack {Q^{1}\left( {P_{e}/4} \right)} \right\rbrack}^{2}\left( {2^{b_{s,n}} - 1} \right)}$describes a target bit error rate (BER).

The non-real-time traffic scheduling operation comprises: checkingwhether unallocated PRBs are present or not if PRBs have been allocatedto all the real-time traffic flows in the real-time traffic schedulingstep; and if, as a result of the checking, the unallocated PRBs arepresent, allocating the unallocated PRBs to the non-real-time trafficflows so that a data throughput becomes a maximum in accordance withadaptive modulation coding (AMC) technology by using the excesstransmission power.

The above-described method may further comprise checking whether or notPRBs have been allocated to all the real-time traffic flows that arewaiting for buffers. Also, the scheduling the downlink pack may be basedat least on capacity of at least one from among the PRBs, and excesschannel gain.

The real-time traffic scheduler may comprise: a scheduling metriccalculator configured to calculate a scheduling metric for combinationsof the real-time traffic flows and available PRBs; a traffic schedulerconfigured to perform a process of selecting a combination of areal-time traffic flow and a PRB having a maximum scheduling metric,calculated by the scheduling metric calculator, on all the pieces ofreal-time traffic.

The scheduling metric calculator calculates the scheduling metric byusing a ratio of an excess channel gain and reception power required perbit.

The apparatus of claim 7, wherein the non-real-time traffic schedulerallocates the PRBs, remaining after the allocation by the real-timetraffic scheduler to all the real-time traffic flows, to thenon-real-time traffic flows so that a data throughput becomes a maximumin accordance with adaptive modulation coding (AMC) technology by usingthe excess transmission power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a construction according to an embodiment for the downlinkof a wireless communication system an exemplary embodiment is applied;

FIG. 2 shows a construction according to an exemplary embodiment of anapparatus for scheduling a downlink packet in a wireless communicationsystem;

FIG. 3 shows a flowchart according to an exemplary embodiment for amethod for scheduling a downlink packet in a wireless communicationsystem; and

FIG. 4 is a diagram showing a relation between a scheduling metric and achannel gain in accordance with an exemplary embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The above aspects, characteristics, and merits will become more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, and thus a person having ordinary skill in theart to which the present disclosure pertains may readily implement thetechnical spirit of the present invention. Furthermore, in describingexemplary embodiments, a detailed description of known art related tothe exemplary embodiments will be omitted if it is deemed to make thegist of the present disclosure unnecessarily vague. Exemplaryembodiments are described in detail below with reference to theaccompanying drawings.

Throughout this specification, when it is described that one part is“connected” to the other part, the one part may be “directly connected”to the other part or “electrically connected” to the other part througha third element. Furthermore, when it is said that any part “includes”or “comprises” any element, it means the part does not exclude otherelements, but may further include or comprise other elements, unlessspecially defined otherwise.

In an exemplary embodiment, in order to select a PRB allocated toreal-time traffic for every scheduling time, a combination havingminimum transmission power per bit, from among all combinations of allreal-time traffic flows and PRBs, is selected. If transmission powerallocated to real-time traffic is minimized by performing scheduling asdescribed above and excess PRBs and excess transmission power are usedto send non-real-time traffic, transmission delay requirements can besatisfied and the data throughput of non-real-time traffic can bemaximized by giving priority to real-time traffic.

FIG. 2 shows a construction according to an exemplary embodiment of anapparatus for scheduling a downlink packet in a wireless communicationsystem.

As shown in FIG. 2, the apparatus for scheduling a downlink packet(downlink scheduler) in a wireless communication system in accordancewith an exemplary embodiment includes a scheduling metric calculationunit 131 for calculating a scheduling metric for all combinations ofreal-time traffic flows waiting for transmission in respective buffersand available physical resource blocks (PRBs), a real-time trafficscheduling unit 132 for performing a process of selecting a combinationof a real-time traffic flow and a PRB, having a maximum calculatedscheduling metric, on all pieces of real-time traffic, and anon-real-time traffic scheduling unit 133 for allocating PRBs remainingafter PRBs are allocated to all the real-time traffic flows, tonon-real-time traffic flows so that the data throughput becomes amaximum in accordance with adaptive modulation coding (AMC) technology,that is, a known adaptive modulation scheme.

Here, in calculating the scheduling metric for the combinations of thereal-time traffic flows and the PRBs, the scheduling metric calculationunit 131 calculates the scheduling metric by utilizing a ratio of anexcess channel gain and reception power required per bit.

Furthermore, the non-real-time traffic scheduling unit 133 allocates allthe remaining PRBs to the non-real-time traffic flows so that the datathroughput becomes a maximum in accordance with adaptive modulationcoding (AMC) technology by using the entire excess transmission power.

FIG. 3 shows a flowchart according to an exemplary embodiment for amethod for scheduling a downlink packet in a wireless communicationsystem. This figure shows a procedure in which the downlink schedulerallocates a corresponding PRB to a traffic flow.

First, a scheduling metric for all combinations of real-time trafficflows waiting in respective buffers and available physical resourceblocks (PRBs) are calculated (21).

Here, in calculating the scheduling metric for the combinations of thereal-time traffic flows and the PRBs, the scheduling metric iscalculated by utilizing a ratio of an excess channel gain and receptionpower required per bit.

Next, a combination of a real-time traffic flow and a PRB having amaximum calculated scheduling metric is selected (22).

Next, it is checked whether a combination of a real-time traffic flowand a PRB has been selected or not in relation to all real-time trafficflows that are waiting for transmission in the buffers (23). That is, itis checked whether or not PRBs has been allocated to all the real-timetraffic flows that are waiting for the buffers.

If, as a result of the check (23), unallocated real-time traffic ispresent, the processes are repeatedly performed starting from theprocess “21”. If PRBs have been allocated to all the real-time trafficflows (i.e., a combination of a real-time traffic flow and a PRB hasbeen selected in relation to all the real-time traffic flows), it ischecked whether unallocated PRBs are present or not (24). That is, it ischecked whether or not there are PRBs remaining after PRBs are allocatedto all the real-time traffic flows that are waiting for transmission inthe buffers.

If, as a result of the check (24), unallocated PRBs are not present, theprocess is terminated. If unallocated PRBs are present (i.e., if thereare PRBs remaining after PRBs are allocated to all the real-time trafficflows waiting for transmission in the buffers), the remaining PRBs(i.e., the unallocated PRBs) are allocated to non-real-time trafficflows so that the data throughput becomes a maximum in accordance withan adaptive modulation coding (AMC) technology, that is, a knownadaptive modulation scheme (25). Here, the remaining PRBs are allocatedto the non-real-time traffic flows so that the data throughput becomes amaximum in accordance with adaptive modulation coding (AMC) technologyby using the entire excess transmission power.

Traffic flows that will use all PRBs are selected for each TTI byperforming downlink packet scheduling as described above.

A detailed exemplary embodiment of the aforementioned method andapparatus for scheduling a downlink packet is described in more detailbelow with reference to FIG. 4.

Transmission power per bit that is expected when a traffic flow s uses aspecific PRB n, is represented in [Equation 3] below.

$\begin{matrix}{\frac{P_{s,n}}{b_{s,n}} = \frac{f\left( b_{s,n} \right)}{g_{s,n}b_{s,n}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, P_(s,n) is transmission power in a base station that is necessaryto send the traffic flow s by b_(s,n) bits through the PRB n, f(b_(s,n))is reception power in user equipment that is necessary to send thetraffic flow s by b_(s,n) bits through the PRB n, and g_(s,n), indicatesa channel gain for the PRB n of downlink corresponding to the trafficflow s. When a target BER is defined as P_(e), f(b_(s,n)) can berepresented as in [Equation 4] below.

$\begin{matrix}{{f\left( b_{s,n} \right)} = {{\frac{\sigma_{s,n}^{2}}{3}\left\lbrack {Q^{- 1}\left( {P_{e}/4} \right)} \right\rbrack}^{2}\left( {2^{b_{s,n}} - 1} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, σ_(s,n) ² indicates a noise variance of the subcarriers of the PRBn in the user equipment that correspond to the traffic flow s,

${Q(x)} = {\frac{1}{\sqrt{2\pi}}{\int_{x}^{\infty}{{\mathbb{e}}^{- \frac{t}{2}}\ {{\mathbb{d}t}.}}}}$

Accordingly, the reception power f(b_(s,n)) in the user equipment thatis necessary to send the traffic flow s by b_(s,n), bits through the PRBn can be calculated more easily than the transmission power P_(s,n) inthe base station that is necessary to send the traffic flow s by b_(s,n)bits through the PRB n. The reception power and the transmission powerhave a proportional relation as in [Equation 3], and thus the exemplaryembodiment is described below by using the reception power f(b_(s,n)) inthe user equipment. This is similar to using the transmission power inthe base station.

Accordingly, a scheduling method of minimizing transmission power perbit can be represented as in [Equation 5] below.

$\begin{matrix}{\left( {\hat{s},\hat{n}} \right) = {\arg\mspace{11mu}{\min\limits_{s,n}\frac{f\left( b_{s,n} \right)}{g_{s,n}b_{s,n}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Furthermore, assuming that a link adaptation scheme is applied to adownlink and the maximum possible transmission power per PRB in the basestation is sufficiently large, [Equation 5] can be represented as in[Equation 6] below

$\begin{matrix}{\left( {\hat{s},\hat{n}} \right) = {\arg\mspace{11mu}{\max\limits_{s,n}\mspace{11mu}{M\left( {s,n} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Here, a scheduling metric M(s,n) for a combination of the traffic flow sand the PRB n is represented as in [Equation 7] below.

$\begin{matrix}{\;{{M\left( {s,n} \right)} = \frac{\Delta_{s,n}}{{f\left( b_{s,n} \right)}/b_{s,n}}}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Here, Δ_(s,n) is an excess channel gain and is defined asΔ_(s,n)=g_(s,n)−g_(min)(b_(s,n)), where g_(min)(b_(s,n)) indicates aminimum channel gain that is necessary to successfully send b_(s,n)bits, and b_(s,n) is the greatest positive integer that satisfiesΔ_(s,n)≧0.

If the downlink scheduler in accordance with an exemplary embodiment iscalled a “minimum power (MP) scheduler”, the MP scheduler allocates thePRB n to the traffic flow of user equipment that has a great excesschannel gain as compared with reception power required per bit based on[Equation 7]. Furthermore, the PRB is allocated to user equipment havingsmaller reception power required per bit, from among pieces of userequipment having the same excess channel gain value.

For example, an instance in which the channel quality indicators (CQI)of pieces of user equipment (UE) i, j, and k are those of FIG. 4 istaken into consideration. FIG. 4 is a diagram showing a relation betweena scheduling metric and a channel gain in accordance with an exemplaryembodiment. In FIG. 4, it is assumed that the pieces of UE k and j areranked as respective MCS levels 1 and 2 and the MCS level 1 means ahigher data rate than the MCS level 2. In this case, the UE k requireslower transmission power per bit than the UE j even though it can sendmore bits than the UE j. This is because the UE k requires lowtransmission power because the CQI of the UE k is much larger than aminimum CQI necessary for the MCS level 1, whereas the UE j requireshigh transmission power as compared with other cases because the CQI ofthe UE j is close to a minimum value necessary for the MCS level 2.

Furthermore, the UE i has an excess channel gain having a similar levelto that of the UE k, but requires reception power per bit that isrelatively lower than that of the UE k. This is because the receptionpower f(b_(s,n))/b_(s,n) required per bit increases exponentiallyaccording to b_(s,n) and thus a reception power value per bit that isnecessary for the UE i is smaller than that of the UE k which has ahigher MCS level than the UE i. Accordingly, the MP scheduler of theexemplary embodiment determines priority in order of the pieces of UE i,k, and j as shown in FIG. 4 in allocating UE that will use the PRB n.

In order to reduce the degree of complexity of the MP scheduler, thescheduling metric of [Equation 7] can be rewritten into [Equation 8]below.

$\begin{matrix}{{M\left( {s,n} \right)} = \frac{g_{s,n} - {g_{\min}\left( b_{s,n} \right)}}{\sigma_{s,n}^{2}{w\left( b_{s,n} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Here, w(b_(s,n)) is equal to [Equation 9] below, and g_(min)(b_(s,n))and b_(s,n) can be previously calculated in relation to all possiblevalues of b_(s,n).

$\begin{matrix}{{w\left( b_{s,n} \right)} = {{\frac{1}{3b_{s,n}}\left\lbrack {Q^{- 1}\left( {P_{e}/4} \right)} \right\rbrack}^{2}\left( {2^{b_{s,n}} - 1} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

As described above, in the exemplary embodiment, in a wirelesscommunication base station, downlink packet scheduling is performed bytaking an MCS level and an excess channel gain into consideration.

Meanwhile, the aforementioned method for scheduling a downlink packet ina wireless communication system in accordance with the exemplaryembodiments can be implemented in the form of a program commandexecutable by various pieces of computer means and recorded on acomputer-recordable medium. The computer-readable medium can include aprogram command, a data file, and a data structure solely or incombination. The program command recorded on the recording medium mighthave been specially designed and configured for the exemplaryembodiments or may be known or available to a person who is skilled incomputer software. Examples of the computer-readable recording mediuminclude a variety of hardware apparatuses that are specially configuredto store and execute a program command, such as magnetic media, such asa hard disk, a floppy disk, and a magnetic tape, optical media, such ascompact disc (CD)-ROM and a digital versatile disc (DVD),magneto-optical media, such as a floptical disk, read-only memory (ROM),random-access memory (RAM), and flash memory. The medium may be atransmission medium, such as light, a metal line, or a waveguideincluding a carrier for sending a signal that designates a programcommand, a data structure, etc. Examples of the program command includea machine code, such as one written by a compiler, and a high-levellanguage code executable by a computer by using an interpreter. Thehardware apparatus can be configured in the form of one or more softwaremodules for performing the operation of the exemplary embodiments, andthe vice versa.

Although the present disclosure has been described in connection withthe limited exemplary embodiments and the drawings, the presentinvention is not limited to the embodiments. A person having ordinaryskill in the art to which the present disclosure pertains cansubstitute, modify, and change the exemplary embodiments withoutdeparting from the technical spirit of the present invention.

Accordingly, the scope of the present invention should not be limited tothe aforementioned exemplary embodiments, but should be defined by theclaims and equivalents thereof.

As described above, an aspect of the exemplary embodiments is that theycan, for example, increase the total data throughput while satisfyingtransmission delay requirements by sending as many pieces of real-timetraffic as possible by using a limited number of PRBs and limitedtransmission power and sending non-real-time traffic using PRBsremaining after allocation to real-time traffic flows and excesstransmission power.

That is, the exemplary embodiments disclosed herein may minimizetransmission power allocated to real-time traffic by selecting acombination of a real-time traffic flow and a PRB having a minimumtransmission power per bit, from all combinations of real-time trafficflows and PRBs in order to select a PRB allocated to real-time trafficfor every scheduling time and may satisfy transmission delayrequirements by the preferential allocation to real-time traffic andmaximize the data throughput of non-real-time traffic by using theremaining PRBs and excess transmission power for the transmission ofnon-real-time traffic.

The exemplary embodiments disclosed herein may be used in downlinkpacket scheduling, etc. in a wireless communication system.

What is claimed is:
 1. A method of scheduling a downlink packet, themethod comprising: a real-time traffic scheduling operation comprisingallocating a physical resource block (PRB) to a traffic flow, whereinthe real-time traffic scheduling operation is performed on all pieces ofreal-time traffic, and the real-time traffic is transmitted by using afirst transmission power in a downlink; and a non-real-time trafficscheduling operation comprising allocating PRBs remaining afterallocation to the real-time traffic in the real-time traffic schedulingoperation, to non-real-time traffic, wherein the non-real-time trafficis transmitted by using a second transmission power in the downlink, thesecond transmission power being an excess transmission power relative tothe first transmission power, and not being used to transmit thereal-time traffic, wherein the real-time traffic scheduling operationcalculates a scheduling metric on all real-time traffic flows, whereinthe real-time traffic scheduling operation and the non-real-time trafficscheduling operation are performed by using an excess channel gain andreception power required per bit.
 2. The method of claim 1, wherein thereal-time traffic scheduling operation further comprises: a metriccalculation operation of calculating the scheduling metric forcombinations of the real-time traffic flows and respective availablePRBs; selecting a combination of a real-time traffic flow and a PRB, thecombination having a maximum calculated scheduling metric; andrepeatedly performing all the processes on all the real-time trafficflows starting from the metric calculation operation.
 3. The method ofclaim 2, wherein the metric calculation operation comprises calculatingthe scheduling metric by using a ratio of the excess channel gain andthe reception power required per bit.
 4. The method of claim 2, whereinthe metric calculation operation comprises calculating the schedulingmetric M(s,n) for a combination of a real-time traffic flow s and a PRBn according to Equation 1, $\begin{matrix}{{{M\left( {s,n} \right)} = \frac{\Delta_{s,n}}{{f\left( b_{s,n} \right)}/b_{s,n}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where Δs,n is the excess channel gain andf(b_(s,n))/b_(s,n) indicates the reception power required per bit. 5.The method of claim 2, wherein the metric calculation operationcomprises calculating the scheduling metric M(s,n) for a combination ofa real-time traffic flow s and a PRB n according to Equation 1,$\begin{matrix}{{{M\left( {s,n} \right)} = \frac{g_{s,n} - {g_{\min}\left( b_{s,n} \right)}}{\sigma_{s,n}^{2}{w\left( b_{s,n} \right)}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where g_(s,n) indicates a channel gain for the PRB n ofdownlink corresponding to the traffic flow s, g_(min)(b_(s,n)) indicatesa minimum channel gain necessary to successfully send b_(s,n) bits,σ_(s,n) ² indicates a noise variance of subcarriers of the PRB n of userequipment corresponding to the traffic flow s, and${w\left( b_{s,n} \right)} = {{\frac{1}{3b_{s,n}}\left\lbrack {Q^{- 1}\left( {P_{e}/4} \right)} \right\rbrack}^{2}\left( {2^{b_{s,n}} - 1} \right)}$describes a target bit error rate (BER).
 6. The method of claim 1,wherein the non-real-time traffic scheduling operation comprises:checking whether unallocated PRB s are present or not, if PRB s havebeen allocated to all the real-time traffic flows in the real-timetraffic scheduling operation; and if, as a result of the checking, theunallocated PRBs are present, allocating the unallocated PRBs tonon-real-time traffic flows so that a data throughput becomes a maximumin accordance with adaptive modulation coding (AMC) technology, by usingthe second transmission power.
 7. The method of claim 6, furthercomprising checking whether or not PRBs have been allocated to all thereal-time traffic flows that are waiting on buffers for transmission. 8.The method of claim 6, wherein if, as a result of the checking, theunallocated PRBs are not present, the scheduling operations are stopped.9. The method of claim 1, wherein the scheduling the downlink packet isbased at least on a transmission capacity of at least one from among thePRBs, and the excess channel gain.
 10. An apparatus for scheduling adownlink packet, the apparatus comprising: real-time traffic schedulerconfigured to allocate a physical resource block (PRB) to a trafficflow, wherein said allocation is performed on all pieces of real-timetraffic, and the real-time traffic is transmitted by using firsttransmission power in a downlink; and non-real-time traffic schedulerconfigured to allocate PRBs remaining after allocation by the real-timetraffic scheduler of the real-time traffic, to non-real-time traffic,wherein the non-real-time traffic is transmitted by using a secondtransmission power, the second transmission power being an excesstransmission power relative to the first transmission power, and notbeing used to transmit the real-time traffic, wherein the real-timetraffic scheduler calculates a scheduling metric on all real-timetraffic flows, wherein the real-time traffic scheduler and thenon-real-time traffic scheduler operate by using an excess channel gainand reception power required per bit.
 11. The apparatus of claim 10,wherein the real-time traffic scheduler comprises: a scheduling metriccalculator configured to calculate the scheduling metric forcombinations of the real-time traffic flows and respective availablePRBs; a traffic scheduler configured to perform a process of selecting acombination of a real-time traffic flow and a PRB, the combinationhaving a maximum scheduling metric and the maximum scheduling metricbeing calculated by the scheduling metric calculator, on all the piecesof real-time traffic.
 12. The apparatus of claim 11, wherein thescheduling metric calculator calculates the scheduling metric by using aratio of between the excess channel gain and the reception powerrequired per bit.
 13. The apparatus of claim 12, wherein the schedulingmetric calculator calculates a scheduling metric for a combination of areal-time traffic flow s and a PRB n according to Equation 1,$\begin{matrix}{{{M\left( {s,n} \right)} = \frac{\Delta_{s,n}}{{f\left( b_{s,n} \right)}/b_{s,n}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where Δs,n is the excess channel gain andf(b_(s,n))/b_(s,n) indicates the reception power required per bit. 14.The apparatus of claim 12, wherein the scheduling metric calculatorcalculates the scheduling metric according to Equation 1,$\begin{matrix}{{{M\left( {s,n} \right)} = \frac{g_{s,n} - {g_{\min}\left( b_{s,n} \right)}}{\sigma_{s,n}^{2}{w\left( b_{s,n} \right)}}},} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$ where, g_(s,n) indicates a channel gain for the PRB n ofdownlink corresponding to the traffic flow s, g_(min)(b_(s,n)) indicatesa minimum channel gain necessary to successfully send b_(s,n) bits,σ_(s,n) ² indicates a noise variance of subcarriers of the PRB n of userequipment corresponding to the traffic flow s, and${w\left( b_{s,n} \right)} = {{\frac{1}{3b_{s,n}}\left\lbrack {Q^{- 1}\left( {P_{e}/4} \right)} \right\rbrack}^{2}\left( {2^{b_{s,n}} - 1} \right)}$describes a target bit error rate (BER).
 15. The apparatus of claim 10,wherein the non-real-time traffic scheduler allocates the PRB s,remaining after the allocation by the real-time traffic scheduler of allthe real-time traffic flows, to the non-real-time traffic flows so thata data throughput becomes a maximum in accordance with adaptivemodulation coding (AMC) technology, by using the second transmissionpower.
 16. The apparatus of claim 15, wherein some of the PRBS areallocated to the real-time traffics flows that are waiting on buffersfor transmission.
 17. The apparatus of claim 10, wherein the schedulingthe downlink packet is based at least on a transmission capacity of atleast one from among the PRBs, and excess channel gain.